U.S. Pat. No. 5,119,898, issued 9 Jan. 1992 and assigned to the assignee of this invention, describes a hydraulic power steering system manufactured by the assignee of this invention, General Motors Corporation, and identified by the tradename MAGNASTEER, including a steering gear in which an electromagnetic mechanism is selectively operable to vary the performance characteristics of a conventional proportional control valve of the steering gear. The proportional control valve includes a valve spool connected to a steering wheel, a valve body around the valve spool connected to a pair of steered wheels, and a torsion bar which resiliently centers the valve spool relative to the valve body. Variable flow area throttling orifices formed between the valve body and valve spool regulate a steering assist boost pressure as a function of the amount of twist of the torsion bar which, in turn, is proportional to the manual effort applied at the steering wheel. A rotary magnetic circuit of the electromagnetic mechanism includes a pair of pole pieces which rotate with the valve body and a permanent magnet assembly which rotates with the valve spool. A stationary exciting coil of the electromagnetic mechanism cooperates with the rotary magnetic circuit to vary the centering force of the torsion bar when the coil is energized. A permanent magnet assembly according to this invention is an improvement relative to the permanent magnet assembly described in the aforesaid U.S. Pat. No. 5,119,898 and embodied in the steering gear of the aforesaid MAGNASTEER steering system.